Two-Transistor Active Pixel Sensor Readout Circuits in Amorphous Silicon Technology for High-Resolution Digital Imaging Applications

Taghibakhsh, Farhad; Karim, K.S.

doi:10.1109/ted.2008.926744

Cited by 26 publications

(11 citation statements)

References 19 publications

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“…The overlap capacitances should be minimized to reduce current modulation by drain-source voltage, if the CG-TFT is not used in the common drain configuration. Our detailed study of 2T-APS pixels incorporating CG-TFTs shows that the pixels are stable over a prolonged operating time of 10 000 hours, and the noise performance of the pixels considerably improves as the result of removing the select transistor (fewer noise sources) and enhanced pixel gain [11]. Such pixels were successfully integrated with a-Se photoconductor for X-ray detection [12].…”

Section: Resultsmentioning

confidence: 94%

Charge-Gated Thin-Film Transistors for High Resolution Digital Imaging Applications

Taghibakhsh

Karim

2008

IEEE Electron Device Lett.

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A field-effect thin-film transistor (TFT) with two gates, which are charge and voltage gates, is introduced. By applying a proper voltage to the voltage gate, the device is biased at a desired operating point or turned on and off, whereas the amount of charge deposited on the charge gate, which is embedded inside the dielectric, shifts the threshold voltage and therefore modulates the drain-source current. Such device finds application in sensor circuits, particularly high resolution sensor arrays, where it replaces both the tranconducting amplifier and the addressing switch transistor, thus reducing transistor count per pixel. Device structure, operation, and characteristics are derived and discussed. A planar configuration of the charge-gated TFT was fabricated by using top-gate amorphous silicon TFTs and implemented in a 100-µm-pitch two-transistor active pixel sensor test structure.Index Terms-Amorphous silicon (a-Si), digital imaging, high resolution, thin-film transistor (TFT).

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Section: Resultsmentioning

confidence: 94%

Charge-Gated Thin-Film Transistors for High Resolution Digital Imaging Applications

Taghibakhsh

Karim

2008

IEEE Electron Device Lett.

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“…It is imperative that the T s is long enough to provide enough charge which is capable to overcome noise elements of the system. The charge gain depends on the transconductance (g m ) of the pixel TFT and the capacitance of the detector, in this case, or the capacitance between the 'virtual gate' and the channel layer C i [6][7].…”

Section: Readout Validationmentioning

confidence: 99%

Novel silicon x-ray detector with TFT readout

Shin

Wang²,

Allec

et al. 2012

SPIE Proceedings

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Crystalline Silicon Drift Detectors (SDDs) have been used for spectroscopy and particle physics applications since they were first reported in the 1980s[1] [2]. However, spatial resolution and a complex fabrication process are two major hurdles that prevent SDDs from seeing widespread use in diffraction imaging and protein crystallography. To overcome the issues with SDDs, we proposed a new type of silicon radiation detector integrated with a hydrogenated amorphous silicon (a-Si:H) thin film transistor (TFT) readout technology intended for low X-ray energy detection with high spatial resolution [3]. This work aims to extend our previous effort by examining in detail the operation of the proposed integrated silicon TFT detector and to evaluate its X-ray sensitive performance via numerical analysis. In this research we simulate a 250-μm-thick slightly doped p-type silicon substrate that also functions as an X-ray detector integrated with a TFT readout having a channel length of 15 μm and a source/drain width of 15 μm. The simulations performed focus on the potential distribution and band structure at the heterostructure interface between the TFT and the silicon detector, and also on the current-voltage characteristics of the TFT due to X-ray exposure. Based on simulation results, the expected lower and upper limits of performance will be presented. In particular, the feasibility of a single 6 keV photon detection (arguably the minimum signal for a crystallography application) with such a device will be examined.

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“…The DCAPS makes use of a current amplifier to improve its speed as opposed to a charge amplifier used for previously reported a-Si APS circuits [3][7] [8]. During readout, the low impedance input terminal of the current amplifier (PerkinElmer 5182) minimizes the effect of the large line capacitance, thus making fast signal readout feasible.…”

Section: Transient Response Of the Dcaps Circuitmentioning

confidence: 99%

“…The larger input voltage causes the APS output to be non-linear thus requiring additional off-panel signal processing. To address this concern, dual mode pixels based on a combination of PPS and APS circuits were reported [7] [8]. However, these circuits do not provide an SNR improvement when the PPS mode is used for larger Xray signals thus limiting potential X-ray dose reduction benefits.…”

Section: Introductionmentioning

confidence: 99%

Characterization of current programmed amorphous silicon active pixel sensor readout circuit for dual mode diagnostic digital x-ray imaging

Safavian

Yazdandoost

et al. 2009

SPIE Proceedings

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A dual mode current-programmed, current-output active pixel sensor (DCAPS) in amorphous silicon (a-Si:H) technology is introduced for digital X-ray imaging, and in particular, for hybrid fluoroscopic and radiographic imagers. Here, each pixel includes an extra capacitor that selectively is coupled to the pixel capacitance to realize the dual mode behavior. Pixel structure, operation and characteristics are presented. The proposed DCAPS circuit was fabricated and assembled using an in-house bottom gate inverted staggered a-Si:H thin film transistor (TFT) process. Gain, lifetime, transient performance as well as noise analysis were carried out. The results are promising and demonstrate that the DCAPS enables dual mode X-ray imaging while compensating for the long term electrical and thermal stress related a-Si TFT threshold voltage (V t ) shift.

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Two-Transistor Active Pixel Sensor Readout Circuits in Amorphous Silicon Technology for High-Resolution Digital Imaging Applications

Cited by 26 publications

References 19 publications

Charge-Gated Thin-Film Transistors for High Resolution Digital Imaging Applications

Charge-Gated Thin-Film Transistors for High Resolution Digital Imaging Applications

Novel silicon x-ray detector with TFT readout

Characterization of current programmed amorphous silicon active pixel sensor readout circuit for dual mode diagnostic digital x-ray imaging

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